Centrifugal fan

ABSTRACT

A centrifugal fan preferably includes a stator portion; a substantially cylindrical rotor holder; an annular support plate secured to an outer circumferential surface and/or a lower end portion of the rotor holder; and a plurality of blades secured to the support plate. The support plate is integrally defined by a substantially annular blade support portion arranged radially farthest from the rotor holder to support the plurality of blades; a cylindrical portion arranged radially closest to the rotor holder to encircle the outer circumferential surface of the rotor holder; and a sloping portion arranged between the blade support portion and the cylindrical portion to slope from an upper end portion of the cylindrical portion to the blade support portion.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a centrifugal fan used for the purpose of air blowing or the like.

2. Description of the Related Art

In conventional centrifugal fans, a plurality of blades are arranged in a circumferential direction with respect to a rotation axis, and a motor is driven to rotate the blades to take in air along an axial direction and discharge the air in a radial direction. The motor includes a stator portion and a rotor portion, and the rotor portion is supported so that it is able to rotate with respect to the stator portion. The blades are secured to a cylindrical rotor holder, and the blades are thereby arranged to rotate together with the rotor holder.

In such conventional centrifugal fans, when the air which has been drawn in along the axial direction is discharged in the radial direction, the flow of air is disturbed near an outer circumferential surface of the rotor holder, and especially at a lower end portion thereof. This disturbance generates noise.

In connection with this type of problem, JP-A 2005-160264 describes a technique to reduce the noise. According to this technique, the outer circumferential surface of the cylindrical rotor holder is arranged to slope to smooth the air flow, thereby reducing the noise.

JP-A 2004-229468 describes another conventional centrifugal fan with a structure that is designed to smooth the air flow.

In addition, JP-A 2007-23877 discloses a technique of providing an annular support plate to support a plurality of blades, and securing the support plate to an opening portion or a side surface of the rotor holder by insert molding.

In order to smooth the air flow, it is desirable that the outer circumferential surface of the rotor holder be arranged to slope in a curved fashion. In this case, however, since the stator portion is arranged inside the rotor holder, an outer circumferential surface of an armature (a winding portion) defining a portion of the stator portion will need to be arranged to slope in accordance with a slope angle of the outer circumferential surface of the rotor holder. As such, the shape of the outer circumferential surface of the armature places a constraint on the shape of the outer circumferential surface of the rotor holder. This makes it practically difficult to provide an arbitrary sloping shape (e.g., a curved shape) to the outer circumferential surface of the rotor holder.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a centrifugal fan includes a stator portion; a substantially cylindrical rotor holder; an annular support plate secured to an outer circumferential surface and/or a lower end portion of the rotor holder, and arranged to spread radially outward from the rotor holder; and a plurality of blades secured to the support plate. The plurality of blades are arranged to be spaced from the outer circumferential surface of the rotor holder and arranged in a circumferential direction with respect to the rotor holder. The support plate is preferably defined by an integral unit including a substantially annular blade support portion arranged radially farthest from the rotor holder to support the plurality of blades; a cylindrical portion arranged radially closest to the rotor holder to encircle the outer circumferential surface of the rotor holder; and a sloping portion arranged between the blade support portion and the cylindrical portion to slope from an upper end portion of the cylindrical portion to the blade support portion.

According to this centrifugal fan, the inclusion of the sloping portion which is arranged to slope, preferably in a curved fashion, radially outward away from the rotor holder in the support plate, to which the blades are secured, contributes to a smooth radial discharge of air which has been taken in along an axial direction without the need to modify the shape of the outer circumferential surface of the rotor holder. Moreover, since the blade support portion, the cylindrical portion, and the sloping portion can be provided integrally (by, for example, molding) to define the support plate, the sloping portion can be defined by any arbitrary shape. Thus, the support plate, which is arranged to produce the aforementioned beneficial effects and contributes to a reduction in noise, can be formed easily, making it possible to manufacture the centrifugal fan with a stable strength at a low cost.

Other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating the structure of a centrifugal fan according to a first preferred embodiment of the present invention.

FIGS. 2A and 2B are a cross-sectional view and a bottom view, respectively, illustrating the structure of a rotor holder according to the first preferred embodiment of the present invention.

FIGS. 3A, 3B, and 3C are a half plan view, a cross-sectional view, and a half bottom view, respectively, of a situation in which a support plate has been secured to the rotor holder according to the first preferred embodiment of the present invention.

FIGS. 4A and 4B are a half plan view and a cross-sectional view, respectively, of a situation in which a support plate has been secured to a rotor holder according to an example variation of the first preferred embodiment of the present invention.

FIGS. 5A and 5B are a half plan view and a cross-sectional view, respectively, of a situation in which a support plate has been secured to a rotor holder according to another example variation of the first preferred embodiment of the present invention.

FIGS. 6A and 6B are a cross-sectional view and a bottom view, respectively, illustrating the structure of a rotor holder according to a second preferred embodiment of the present invention of the present invention.

FIGS. 7A and 7B are a cross-sectional view and a half bottom view, respectively, of a situation in which a support plate has been secured to the rotor holder according to the second preferred embodiment of the present invention.

FIGS. 8A and 8B are a cross-sectional view and a bottom view, respectively, illustrating the structure of a rotor holder according to an example variation of the second preferred embodiment of the present invention.

FIG. 9 is a bottom view illustrating the structure of a support plate according to another preferred embodiment of the present invention.

FIG. 10A is a cross-sectional view illustrating the structure of blades according to this preferred embodiment of the present invention.

FIG. 10B is a cross-sectional view of a situation in which the support plate has been secured to a rotor holder according to this preferred embodiment of the present invention.

FIG. 11A is a perspective view illustrating the structure of the blades according to this preferred embodiment of the present invention.

FIG. 11B is a perspective view of a situation in which the support plate has been secured to the rotor holder according to this preferred embodiment of the present invention.

FIG. 11C is a perspective view of a situation in which the blades have been secured to the support plate according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to the preferred embodiments described below, and that variations and modifications can be made appropriately as long as desired effects and arrangements of the present invention are not impaired. Also note that the preferred embodiments described below may be combined with other embodiments. For the sake of convenience, it is assumed herein that an upward/downward direction is defined by a direction moving along a central axis J, and that a side on which a base portion 41 described below is arranged is referred to as a lower side, while the opposite side along the central axis J is referred to as an upper side. Note that the central axis J may not necessarily be in parallel with the direction of gravity and can be arranged in any direction.

First Preferred Embodiment

FIG. 1 is a cross-sectional view of a centrifugal fan according to a first preferred embodiment of the present invention, taken along a plane including the central axis J.

As illustrated in FIG. 1, the centrifugal fan preferably includes a rotor portion 3, a stator portion 4, and a plurality of blades 10. The stator portion 4 is arranged to support the rotor portion 3 such that the rotor portion 3 is rotatable about the central axis J. The blades 10 are fixed in relation to the rotor portion 3.

The rotor portion 3 preferably includes a rotor holder 31 and a field magnet 32. The rotor holder 31 is substantially defined by the shape of a covered cylinder. The field magnet 32 is secured to an inside of a side wall portion of the rotor holder 31. The stator portion 4 includes the base portion 41, an armature 42, and a bearing support portion 43. The bearing support portion 43 is arranged to protrude upward from the base portion 41. The armature 42 is secured to an outer surface of the bearing support portion 43. Ball bearings 52 are arranged at upper and lower positions along the central axis J inside the bearing support portion 43.

An annular support plate 2 is secured to an outer circumferential surface and/or a lower end portion of the rotor holder 31. The support plate 2 is arranged to spread radially outward from the rotor holder 31 and support the blades 10. The blades 10 are arranged in a circumferential direction with respect to the rotor holder 31, and secured to the support plate 2. The blades 10 are spaced from the outer circumferential surface of the rotor holder 31. The support plate 2 and the blades 10 together define an impeller portion.

A bushing 51 is secured to a center of a cover portion of the rotor holder 31, and a shaft 50 is preferably press fitted, for example, into the bushing 51. The shaft 50 is inserted inside the bearing support portion 43, and rotatably supported by the ball bearings 52. Here, the shaft 50 and the ball bearings 52 together define a bearing mechanism to support the rotor portion 3 and the blades 10 such that the rotor portion 3 and the blades 10 are rotatable with respect to the stator portion 4.

In the centrifugal fan having the above-described structure, a drive current is supplied to the armature 42 to produce a torque centered on the central axis J between the armature 42 and the field magnet 32, so that the blades 10, which are fixed in relation to the rotor holder 31, rotate about the central axis J together with the shaft 50 secured to the rotor holder 31.

In the present preferred embodiment, the support plate 2, which is secured to the outer circumferential surface and/or the lower end portion of the rotor holder 31, preferably includes three portions. Specifically, the support plate 2 preferably has an integral structure including a substantially annular blade support portion 21, a cylindrical portion 22, and a sloping portion 23. The blade support portion 21 is arranged radially farthest from the rotor holder 31 to support the blades 10. The cylindrical portion 22 is arranged in contact with the outer circumferential surface of the rotor holder 31. The sloping portion 23 is arranged between the cylindrical portion 22 and the blade support portion 21 to slope in a curved fashion from an upper end portion of the cylindrical portion 22 to the blade support portion 21. The support plate 2 is arranged to assume a smooth curve in cross section from the cylindrical portion 22 to a radially outermost portion of the support plate 2.

The inclusion of the sloping portion 23, which is arranged to slope in a curved fashion while extending radially outward away from the outer circumferential surface of the rotor holder 31, in the support plate 2 arranged to support the blades contributes to a smooth radial discharge of air which has been taken in along an axial direction. In addition, the inclusion of the cylindrical portion 22, which is arranged in contact with the outer circumferential surface of the rotor holder 31, in the support plate 2 contributes to firm and reliable securing of the support plate 2 to the rotor holder 31. Moreover, since the blade support portion 21, the cylindrical portion 22, and the sloping portion 23, which together define the support plate 2, are preferably defined integrally, (by, for example molding) with one another, the sloping portion 23 can be constructed in an arbitrary shape. Thus, the support plate 2 can be easily formed and still is capable of producing the aforementioned beneficial effects. It is thus possible to manufacture the centrifugal fan at a low cost while maintaining stable strength thereof and achieving a noise reduction.

In the present preferred embodiment, it is preferable that the securing of the support plate 2 to the rotor holder 31 be accomplished by, for example, insert molding. The insert molding according to the present preferred embodiment will now be described in detail below, but any other desirable manufacturing method could be used.

FIGS. 2A and 2B are a cross-sectional view and a bottom view, respectively, illustrating the structure of the rotor holder 31 according to the present preferred embodiment.

The rotor holder 31 preferably has, at the lower end portion thereof, a protruding portion (a flange portion) 33 arranged to protrude radially outward from the rotor holder 31. The protruding portion 33 is preferably insert-molded with a lower end portion of the cylindrical portion 22 of the support plate 2, so that the support plate 2 is secured to the rotor holder 31. However, the protruding portion 33 could be provided through any desirable method.

The support plate 2 can be easily integrally defined by the blade support portion 21, the cylindrical portion 22, and the sloping portion 23 by injection molding or the like, using two molds which are separated from each other along the central axis J for mold release. As illustrated in FIG. 1, this allows the cylindrical portion 22 to have a wall thickness substantially equal to the protruding extent of the protruding portion 33.

The protruding extent of the protruding portion 33 needs to be constant around the circumference of the rotor holder 31, in order for the support plate 2 to be secured to the rotor holder 31 with a constant strength around the circumference of the rotor holder 31. This may lead to the cylindrical portion 22 having a thickness greater than that of the blade support portion 21 and the sloping portion 23. In this case, at the time of the injection molding, the greater-thickness cylindrical portion 22 may undergo a deformation (or the occurrence of a sink mark) as a result of mold shrinkage. When the cylindrical portion 22 experiences such a deformation, the strength with which the support plate 2 is secured to the rotor holder 31 may be reduced, and in some cases, the cylindrical portion 22 may even experience a breakage.

An effective measure against this problem will now be described below with reference to FIGS. 3A, 3B, and 3C. FIGS. 3A, 3B, and 3C are a half plan view, a cross-sectional view, and a half bottom view, respectively, of a situation in which the support plate 2 has been secured to the rotor holder 31.

As illustrated in FIG. 3B, the cylindrical portion 22 preferably has an annular thickness reducing portion 24 a defined therein so as to extend downward from an axially upper end thereof. As mentioned above, the support plate 2 can be integrally defined by the blade support portion 21, the cylindrical portion 22, and the sloping portion 23 by the injection molding, preferably using two molds which are separated from each other along the central axis J for mold release. Therefore, it is easy to define the thickness reducing portion 24 a so as to extend along the central axis J by placing in the two molds an insert mold designed to define the thickness reducing portion 24 a. The provision of the thickness reducing portion 24 a enables the cylindrical portion 22 to have a thickness substantially equal to that of the sloping portion 23, and contributes to preventing the cylindrical portion 22 from experiencing a deformation (or having a sink mark) as a result of mold shrinkage, at the time of the injection molding.

Referring to FIG. 3C, joint portions 25, which are defined on a lower side of the protruding portion 33 as a result of the insert molding, are arranged at regular intervals in the circumferential direction. Note, however, that this is not essential to the present invention, and that a joint portion may be arranged in a ring shape.

Notice here that the provision of the thickness reducing portion 24 a in the cylindrical portion 22 results in a corresponding reduction in the thickness of the cylindrical portion 22. This may lead to a decrease in the strength with which the support plate 2 is secured to the rotor holder 31.

As a measure against this problem, it is preferable that, as illustrated in FIG. 3A, the thickness reducing portion 24 a be defined by a plurality of subportions spaced from one another in the circumferential direction. In this case, as illustrated in FIG. 3B, the cylindrical portion 22 maintains a thickness substantially equal to the protruding extent of the protruding portion 33, at circumferential positions where no thickness reducing portion 24 a is provided. The strength with which the support plate 2 is secured to the rotor holder 31 is thus reinforced at these greater-thickness portions of the cylindrical portion 22. Note that the number of aforementioned subportions of the thickness reducing portion 24 a may be determined appropriately in accordance with the desired strength with which the support plate 2 is to be secured to the rotor holder 31.

In the present preferred embodiment, the cylindrical portion 22 of the support plate 2 is preferably arranged in contact with the outer circumferential surface of the rotor holder 31. As illustrated in FIG. 1, the radial thickness of the cylindrical portion 22 does not need to be constant along its axial extent. Furthermore, the cylindrical portion 22 does not need to be arranged in contact with an entire axial extent of the outer circumferential surface of the rotor holder 31, but only needs to be arranged in contact with a sufficient range of the axial extent of the outer circumferential surface of the rotor holder 31 to secure a sufficient strength with which the support plate 2 is secured to the rotor holder 31.

Furthermore, as illustrated in FIGS. 4A and 4B, the cylindrical portion 22 does not need to be arranged in contact with an entire circumferential extent of the outer circumferential surface of the rotor holder 31, but there may be a gap between an inner circumferential portion of the cylindrical portion 22, which opposes the rotor holder 31, and an outer circumferential portion of the rotor holder 31. As illustrated in FIGS. 5A and 5B, this gap may be arranged to extend across the entire circumferential extent of the outer circumferential surface of the rotor holder 31.

In the present preferred embodiment, the support plate is preferably arranged to assume a smooth curve in cross section from the cylindrical portion 22 to the radially outermost portion of the support plate 2. Note, however, that the support plate 2 may also be arranged to assume a straight line in cross section from a radially outermost portion of the sloping portion 23 to the radially outermost portion of the support plate 2 if so desired.

As illustrated in FIG. 1, the rotor holder 31 according to the present preferred embodiment preferably is substantially in the shape of a covered cylinder. Note, however, that the rotor holder 31 may be substantially in the shape of a cylinder without a cover. In this case, the support plate 2 is arranged to cover an axially upper side of the rotor holder 31 entirely, for example, and the shaft 50 is secured to the support plate 2 so as to be coaxial with the rotor holder 31. In more detail, the shaft 50 is insert-molded with the support plate 2.

Furthermore, as illustrated in FIG. 1, in the present preferred embodiment, the support plate 2 is secured to the rotor holder 31 at the lower end portion thereof. Note that the “lower end portion” refers to not only a lower end of the rotor holder 31 but also a neighborhood thereof. Therefore, the protruding portion 33, which protrudes radially outward from the rotor holder 31, may be provided not only at the lower end of the rotor holder 31 as illustrated in FIG. 2A, but also at the neighborhood thereof.

Furthermore, in the present preferred embodiment, the protruding portion 33 is preferably insert-molded with the lower end portion of the cylindrical portion 22 of the support plate 2, so that the support plate 2 is secured to the rotor holder 31. Note, however, that the support plate 2 may be secured to the rotor holder 31 by other methods than the insert molding. Examples of such other methods include press fit, adhesion, heat welding, and ultrasonic welding, for example.

Furthermore, in the present preferred embodiment, the blades 10 may be integrally molded with the support plate 2. In this case, the blades 10 may be integrally molded with the support plate 2 while at the same time the protruding portion 33 is insert-molded with the lower end portion of the cylindrical portion 22 of the support plate 2, so that the blades 10 are fixed in relation to the rotor holder 31 at the same time.

Furthermore, as illustrated in FIG. 1, in the present preferred embodiment, an axial center of the impeller portion, which is defined by the combination of the support plate 2 and the blades 10, and an axial center of the rotor holder 31 are not displaced significantly with respect to each other. Therefore, the centrifugal fan according to the present preferred embodiment is capable of achieving a reduction in axial dimension in comparison to centrifugal fans in which the axial center of the impeller portion and the axial center of the rotor holder are displaced significantly with respect to each other.

Second Preferred Embodiment

In the first preferred embodiment, the thickness reducing portion 24 a is preferably defined in a portion of the cylindrical portion 22 of the support plate 2 to make the thickness of the cylindrical portion 22 substantially equal to the thickness of the sloping portion 23. Notice here that, as illustrated in FIG. 3B, the thickness reducing portion 24 a can be defined only so as to extend downward from the axially upper end of the cylindrical portion 22. This is because the insert mold designed to define the thickness reducing portion 24 a cannot be inserted from a lower side of the rotor holder 31, because the protruding portion 33, which is provided at the lower end portion of the rotor holder 31, is formed in a ring shape as illustrated in FIG. 2B.

In a second preferred embodiment of the present invention, a thickness reducing portion is preferably defined so as to extend upward from the axially lower side. A method for defining such a thickness reducing portion will now be described below with reference to FIGS. 6A, 6B, 7A, and 7B. The structure of a centrifugal fan according to the present preferred embodiment is similar to that of the centrifugal fan according to the first preferred embodiment, except for structural features characteristic of the centrifugal fan according to the present preferred embodiment as described below.

FIGS. 6A and 6B are a cross-sectional view and a bottom view, respectively, illustrating the structure of the rotor holder 31 according to the present preferred embodiment. FIGS. 7A and 7B are a cross-sectional view and a half bottom view, respectively, of a situation in which the support plate 2 has been secured to the rotor holder 31, according to the present preferred embodiment.

As illustrated in FIGS. 6A and 6B, the rotor holder 31 according to the present preferred embodiment preferably has, at the lower end portion thereof, a plurality of protruding portions 33 arranged to protrude radially outward and spaced from one another in the circumferential direction. In addition, as illustrated in FIGS. 7A and 7B, the protruding portions 33 are insert-molded with the lower end portion of the cylindrical portion 22 of the support plate 2, so that the support plate 2 is secured to the rotor holder 31.

Since the protruding portions 33, which are provided at the lower end portion of the rotor holder 31, are spaced from one another in the circumferential direction, an insert mold designed to define a thickness reducing portion can be inserted from the lower side of the rotor holder 31 at any circumferential position where no protruding portion 33 is provided. Therefore, as illustrated in FIG. 7A, it is easy to define a thickness reducing portion 24 b on a side of the cylindrical portion 22 facing the sloping portion 23 so as to extend upward from the axially lower end of the cylindrical portion 22, at any circumferential position where no protruding portion 33 is provided. In this case, the thickness reducing portion 24 b is defined so as to extend upward from the lower side of the rotor holder 31. Therefore, the thickness reducing portion 24 b does not exist within a flow path of air which has been taken in along the axial direction, which permits the air to flow smoothly.

In the present preferred embodiment, as illustrated in FIG. 7B, the cylindrical portion 22 preferably includes, at positions corresponding to the protruding portions 33, columnar increased thickness portions 22 a arranged to protrude radially outward. The circumferential width of the protruding portions 33 is adjusted to make the circumferential dimension of the increased thickness portions 22 a substantially equal to the thickness of the sloping portion 23 and the thickness of the cylindrical portion 22 where no increased thickness portion 22 a is provided. This adjustment prevents the increased thickness portions 22 a from experiencing a deformation (or the formation of a sink mark) as a result of mold shrinkage, at the time of the injection molding.

In the present preferred embodiment, no particular limitations are placed on the shape or number of the protruding portions 33 which are spaced from one another in the circumferential direction. For example, as illustrated in FIGS. 8A and 8B, each of the protruding portions 33 may be arranged to have a smooth curved line.

Other Preferred Embodiments

FIG. 9 is a bottom view illustrating the structure of a support plate 2 according to another preferred embodiment of the present invention. In the case where the blades 10 are not integrally molded with the support plate 2, it is necessary to secure the blades 10 to the blade support portion 21 of the support plate 2. In this case, a plurality of grooves 21 b each in the shape of a circular arc (see FIG. 11B) may be defined in a spiral arrangement on an upper surface of the blade support portion 21. In this case, as illustrated in FIG. 9, the blade support portion 21 has, on a lower surface thereof, protruding portions 21 a corresponding to the grooves 21 b defined on the upper surface thereof. The blades 10 are fit into the grooves 21 b provided in the blade support portion 21, and fixed to the blade support portion 21 by heat welding, ultrasonic welding, or the like, for example.

FIG. 10A is a cross-sectional view illustrating the structure of the blades 10 according to this preferred embodiment. FIG. 10B is a cross-sectional view of a situation in which the support plate 2 has been secured to the rotor holder 31. FIG. 11A is a perspective view illustrating the structure of the blades 10. FIG. 11B is a perspective view of a situation in which the support plate 2 has been secured to the rotor holder 31. FIG. 11C is a perspective view of a situation in which the blades 10 have been secured to the support plate 2.

As illustrated in FIGS. 10A and 11A, the blades 10 are joined to one another at upper ends thereof with an annular shroud 63. Moreover, an annular reinforcing ring (hereinafter referred to as an “outer reinforcing ring”) 60 is preferably attached to a lower end portion of a radially outer end of each blade 10, to prevent a deformation of the blades 10.

In a case where both axial and radial dimensions of the blades 10 are large, the outer reinforcing ring 60 alone may not be sufficient to prevent a deformation of the blades 10. As illustrated in FIGS. 10A and 11A, an additional annular reinforcing ring (hereinafter referred to as an “inner reinforcing ring”) 61 may be attached to a lower end portion of a radially inner end of each blade 10 to prevent a deformation of the blades 10.

When the inner reinforcing ring 61 exists within the flow path of air which has been taken in along the axial direction, the flow of air may be disturbed thereby. Accordingly, as illustrated in FIGS. 10B and 11B, a ring groove 62 designed to accommodate the inner reinforcing ring 61 may be defined on the upper surface of the blade support portion 21 of the support plate 2. In this case, when the blades 10 have been secured to the support plate 2 as illustrated in FIG. 11C, the inner reinforcing ring 61 is embedded in the ring groove 62, preventing a disturbance of the air flow.

Since the outer reinforcing ring 60 is attached to the radially outer ends of the blades 10, the outside diameter of the centrifugal fan increases correspondingly. When the inner reinforcing ring 61 is attached to the radially inner ends of the blades 10, sufficient reinforcement can be obtained even if the radial dimension of the outer reinforcing ring 60 is reduced correspondingly. Therefore, the attachment of the inner reinforcing ring 61 enables a decrease in the radial dimension of the outer reinforcing ring 60, and increases design flexibility in the radial dimension of the centrifugal fan. Note that only the inner reinforcing ring 61 may be attached to the blades 10, without the attachment of the outer reinforcing ring 60.

Also note that a thickness reducing portion may be defined to extend downward from the axially upper end of the cylindrical portion, with the use of the rotor holder according to the second preferred embodiment.

While preferred embodiments of the present invention have been described above, it is to be understood that the foregoing description is in all aspects illustrative and not restrictive, and that a variety of modifications are possible. For example, in the above-described preferred embodiments, a bearing mechanism of a ball bearing type is preferably used as a bearing mechanism for a motor, for example. Note, however, that an oilless bearing using a sleeve may be used in other preferred embodiments, for example.

While preferred embodiments of the present invention have been described above, these are illustrated only by way of example, and it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims. 

1. A centrifugal fan comprising: a stator portion; a substantially cylindrical rotor holder; an annular support plate secured to an outer circumferential surface and/or a lower end portion of the rotor holder, and arranged to spread radially outward from the rotor holder; and a plurality of blades secured to the support plate, arranged to be spaced from the outer circumferential surface of the rotor holder, and arranged in a circumferential direction with respect to the rotor holder; wherein the support plate defined by an integral structure including: a substantially annular blade support portion arranged radially farthest from the rotor holder to support the plurality of blades; a cylindrical portion arranged radially closest to the rotor holder to encircle the outer circumferential surface of the rotor holder; and a sloping portion arranged between the blade support portion and the cylindrical portion to slope from an upper end portion of the cylindrical portion to the blade support portion.
 2. The centrifugal fan according to claim 1, wherein the rotor holder includes, at the lower end portion thereof, a protruding portion arranged to protrude radially outward from the rotor holder, and arranged to be insert-molded with a lower end portion of the cylindrical portion of the support plate, so that the support plate is secured to the rotor holder.
 3. The centrifugal fan according to claim 1, wherein the cylindrical portion includes a first thickness reducing portion defined therein to extend downward from an axially upper end thereof.
 4. The centrifugal fan according to claim 3, wherein the first thickness reducing portion is defined by a plurality of subportions spaced from one another in the circumferential direction.
 5. The centrifugal fan according to claim 3, wherein the first thickness reducing portion is defined in a ring shape to surround the rotor holder.
 6. The centrifugal fan according to claim 3, wherein the cylindrical portion and the sloping portion have substantially the same thickness.
 7. The centrifugal fan according to claim 2, wherein the protruding portion is defined by a plurality of subportions spaced from one another in the circumferential direction, the plurality of subportions of the protruding portion being insert-molded with the lower end portion of the cylindrical portion of the support plate, whereby the support plate is secured to the rotor holder; and the cylindrical portion includes, at positions corresponding to the plurality of subportions of the protruding portion, columnar increased thickness portions arranged to protrude radially outward.
 8. The centrifugal fan according to claim 7, wherein at a circumferential position where no subportion of the protruding portion is provided, the cylindrical portion includes a second thickness reducing portion defined on a side thereof facing the sloping portion to extend upward from an axially lower end of the cylindrical portion.
 9. The centrifugal fan according to claim 7, wherein the cylindrical portion includes substantially the same thickness as that of the sloping portion, except at positions where the increased thickness portions are provided.
 10. The centrifugal fan according to claim 7, wherein each of the increased thickness portions includes a circumferential dimension substantially equal to the thickness of the sloping portion and the thickness of the cylindrical portion where no increased thickness portion is provided.
 11. The centrifugal fan according to claim 1, wherein the plurality of blades are integral with the support plate.
 12. The centrifugal fan according to claim 1, wherein the stator portion is arranged radially inward of the cylindrical portion.
 13. The centrifugal fan according to claim 1, wherein an inner circumferential portion of the cylindrical portion is in contact with an outer circumferential portion of the rotor holder.
 14. The centrifugal fan according to claim 1, wherein the cylindrical portion and the rotor holder are arranged to define a gap between an inner circumferential portion of the cylindrical portion and an outer circumferential portion of the rotor holder.
 15. The centrifugal fan according to claim 1, wherein the sloping portion is arranged to slope in a curved configuration. 